Further Study NEW HIGH PERFORMANCE TITANIUM FOR EXHAUST SYSTEMS TAKASHI YASHIKI SEPTEMBER 2005 TITANIUM TECHNOLOGY DEPARTMENT

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1 NEW HIGH PERFORMANCE TITANIUM FOR EXHAUST SYSTEMS Further Study SEPTEMBER 2005 TAKASHI YASHIKI TITANIUM TECHNOLOGY DEPARTMENT 1

2 Titanium exhaust systems for motorbikes and cars More than 1000 metric tons of Gr.2 are used for motorbike exhaust systems per year throughout the world. Reason : Light weight, High class image, Characteristic titanium color However, titanium exhaust systems have not been used for mass-produced cars. One of the reasons : Car exhaust systems are exposed to higher temperatures than motorbike exhaust systems. These higher temperatures lead to a cracking problem in the exhaust systems -Insufficient high temperature oxidation resistance of Gr.2 -Insufficient high temperature strength of Gr.2. In motorbikes, the exhaust gas temperature also tends to increase Reason : Increase of demand of higher power engine, Use of catalyzer Cracking problem has also been considered recently. 2

3 KOBE STEEL s new titanium alloy series for exhaust systems Ti-1.5Al (Gr.37) The first mass-produced titanium alloy for exhaust systems in the world Mainly for motorbikes with higher exhaust gas temperatures Being mass-produced Registered in ASTM as Gr.37 Ti-1.2ASNEX Mainly for cars and motorbikes with much higher exhaust gas temperatures Superior performance to Ti-1.5Al Already produced mass-produced cold coils (6 metric tons) 3

4 Alloy design concepts Ti-1.5Al (Gr.37) Ti-1.2ASNEX Physical properties Formability The same level as Gr.2 The same level as Gr.2 Strength High temp. oxidation resistance Room temp. High temp. Applicable temp. The same level as Gr.2 Good formability equivalent to Gr.2 2 to 3 times higher than Gr.2 Weight reduction by reducing thickness Higher than Gr.2 Higher than Ti-1.5Al Gr.2 <600 o C o C o C Potential applications Replacement of parts made of Gr.2 Parts which could not be made of titanium due to its lack of high temp. oxidation resistance 4

5 SUZUKI GSX-R1000 Photo: Courtesy of Suzuki Motor Corporation Ti-1.5Al has already been used for mass-produced motorbikes. 5

6 Ti-1.5Al mass-produced exhaust systems made by Akrapovic Akrapovic in Slovenia is one of the most famous motorbike exhaust systems makers in the world. They are the greatest user of Ti-1.5Al. They use Ti-1.5Al for exhaust systems as a standard material instead of Gr.2. More than 150 metric tons of Ti-1.5Al have been produced for their exhaust systems. Photo: Courtesy of Akrapovic Company 6

7 Evaluation results of Ti-1.5Al exhaust system after endurance test Investigated cross section of Ti-1.5Al exhaust system after endurance test Ti-1.5Al Ti-1.5Al -Depression of grain growth -No surface cracks because of excellent oxidation resistance High-endurance is expected No cracks 200μm Gr.2 Welded Gr.2 4m m -Remarkable grain growth -Many surface cracks due to embrittlement by oxidation Breakage is possible in an early stage Cracks 200μm 7

8 Weight gain due to high temperature oxidation Weight gains of these materials are almost the same. Weight gain due to oxidation (mg/cm 2 ) Weight gain of Gr.2 is twice as large as that of Ti-1.2ASNEX. Gr.2 Ti-1.5Al Oxidation temperature ( o C) Ti-1.2ASNEX High temperature oxidation resistance Ti-1.2ASNEX > Ti-1.5Al > Gr.2 Excellent! Exfoliation of titanium oxide scale Only Ti-1.2ASNEX shows a dramatically small weight gain. 8

9 Thickness reduction and grain growth Cross sectional microstructures before and after exposure in air at 800 o C for 100hrs Gr.2 Before test After 800 o C, 100hrs Scale loss Remarkable Thickness reduction and grain growth -Large thickness reduction leads to a decrease of strength. -Too much grain growth leads to low fatigue strength. Ti-1.2ASNEX is the most advantageous material in respect of less deterioration of strength and high fatigue strength. KOBE STEEL, LTD Proprietary Information Ti-1.5Al Ti-1.2ASNEX Level of thickness reduction and grain growth is not as much as with Gr.2 Almost no thickness reduction and no grain growth 9

10 Embrittlement resistance Welded tubes (O.D. 38.1X1.5 t ) 800 o C, 100hrs in air Flattening until cracking Welded tube d 38.1 Gr.2 Ti-1.5Al Ti-1.2ASNEX Flat ratio (%) Flat ratio =(38.1-d)/38.1X100 Brittly cracked 13 Brittly cracked o C is too high for Ti-1.5Al. Not brittly cracked 21 Ti-1.2ASNEX has superior embrittlement resistance. 10

11 Ti-1.2ASNEX exhaust system made by Akrapovic After endurance test Several parts of exhaust systems made of Ti-1.2ASNEX Photo: Courtesy of Akrapovic Company Ti-1.2ASNEX has sufficient formability for making exhaust systems. 11

12 Ti-1.2ASNEX exhaust system made by Akrapovic after endurance test Approx. 800 o C Test conditions -HONDA CRF450 -Tested by Jaka Moze MX3 world motocross championship rider -Total 30hrs, Max temperature approx. 800 o C Gr.2 exhaust systems surely crack in this condition. 12

13 Detailed appearance of Ti-1.2ASNEX exhaust system made by Akrapovic after endurance test Ti-1.2ASNEX exhaust system does not show any damages. 13

14 Inside of Ti-1.2ASNEX exhaust system made by Akrapovic after endurance test Inside of exhaust system does not show any damages. 14

15 Microstructure of Ti-1.2ASNEX exhaust system made by Akrapovic after endurance test Investigated cross section Approx. 800 o C Cross sectional microstructure Total elongations of tensile test pieces sampled from exhaust systems before and after endurance test Before endurance test After endurance test Total elongation 37.5% 37.2% Tensile test piece -Microstructure of exhaust system does not show any damages. -Fine grains are maintained. Inner surface of exhaust pipe Tested test piece sampled from exhaust system after endurance test No decrease of total elongation No embrittlement Long life of exhaust systems is expected by using Ti-1.2ASNEX. 15

16 Conclusions Ti-1.5Al (Gr.37) The first mass-produced titanium alloy for exhaust systems in the world Mainly for motorbikes with higher exhaust gas temperatures High performance and reliability are obtained without much additional cost. Ti-1.2ASNEX Mainly for cars and motorbikes with higher exhaust gas temperatures Vastly improved high temp. oxidation resistance compared with Ti-1.5Al This alloy can be used for parts for which titanium can not be used due to excessive temperatures. 16

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